A piston engine comprises several cylinders in which pistons are stroke-adjustably arranged and in which combustion chambers are formed. A fresh air system serves for the feeding of fresh air to the cylinders. An exhaust system serves for the discharge of exhaust gas from the cylinders. During a gas exchange, exhaust gas formed following a combustion process is discharged from the cylinder and fresh air for the next combustion process supplied. For controlling the gas exchange, gas exchange valves, namely inlet valves and exhaust valves are usually provided.
For performance increase and efficiency improvement as well as emission reduction it is known to utilise dynamic flow effects which develop in the fresh air system for the gas exchange. Through the gas exchange processes vibrations occur in the fresh air system. Through resonant or pulse tubes resonance effects can be utilised in order to improve the charging of the cylinders with fresh air. In order to be able to achieve such a charge improvement also at different rotational speeds of the piston engine, adjustable pulse tubes are generally known, with which for low rotational speeds of the piston engine a comparatively large pulse tube length can be adjusted, while for higher rotational speeds of the piston engine a comparatively short pulse tube length can be adjusted.
In addition, different charging devices are known such as for example compressors and turbochargers, with which the pressure level in the fresh air fed to the cylinders can be increased. The charging of the cylinders can also be improved through this.
On the one hand, cleaning of the exhaust gases in order to reduce the emission values of the piston engine takes place in the exhaust system. On the other hand, damping of the sound generated by the piston engine and carried along in the exhaust gas also takes place in the exhaust system in order to reduce a sound emission of the piston engine. With modern exhaust systems active silencers, which are based on the principle of the anti-sound generation, can also be utilised. Such an active silencer contains at least one electroacoustic converter, which, as a rule, can be a loudspeaker, with the help of which anti-sound is actively generated, which with respect to the sound to be damped is phase-shifted in such a manner that upon the superimposition of sound and anti-sound as large as possible a mutual deletion is obtained. Such active silencers can be used with a fresh air system in order to dampen sound of the piston engine emitted on the fresh air side.